California ADU rules · Santa Clara County
Can I Build an ADU in Los Altos?
Yes — you can build an ADU in Los Altos. California's statewide ADU law requires every city, including Los Altos, to approve a qualifying accessory dwelling unit by right, plus a junior ADU (JADU) on a single-family lot. What varies city to city are the local specifics below.
Can you build one?
ADUs allowed
CA state lawYes — by right
ADUs and JADUs are allowed by right in all residential and mixed-use zones; ministerial approval, no hearing.
Units on a single-family lot
Local rule1 attached ADU + 1 detached ADU + 2 JADUs
Allows 2 JADUs per single-family lot, and both 1 attached and 1 detached ADU.
Units on a multifamily lot
Local ruleconversions (>=1 or 25% of units) + up to 2 detached
Limits detached ADUs on multifamily lots to 2 per lot.
Junior ADU (JADU)
Local ruleAllowed
JADUs allowed; up to 2 per single-family lot.
Size & height
Max detached ADU size
Local rule1,200 sq ft
1,200 sq ft for 2+ bedrooms; 850 sq ft for 1 bedroom. Basement area excluded from calculation.
Max attached ADU size
Local rule850 (1 bedroom) or 1,200 (2+ bedrooms), but not more than 50% of primary; attached ADU of 850 sq ft or less cannot be denied
Local code mirrors state but clarifies 850/1,200 sq ft caps by bedroom count.
Guaranteed minimum size
CA state law800 sq ft
An 800 sq ft ADU must be allowed regardless of FAR/lot-coverage caps; a city also cannot cap an attached ADU below 850 sq ft (1,000 for 2+ bedrooms).
Max JADU size
Local rule500 sq ft
500 sq ft max, including any ingress/egress expansion.
Max height
Local rule20 ft
20 ft for one-story ADUs; 27 ft for two-story; flag lots 20 ft. State minimums apply if more permissive.
Setbacks
Side setback
Local rule4 ft
4 ft minimum side setback for ADUs.
Rear setback
Local rule4 ft
4 ft minimum rear setback for ADUs.
Front setback
Local ruleper base zone unless physically precluded; then city must allow ADU elsewhere
Front setback per base zone, but city must allow ADU if no feasible location.
Separation from main house
CA state lawNone required
No statewide separation requirement between the ADU and the primary dwelling.
Parking
Parking required
Local ruleUp to 1 space
1 uncovered space required for new detached ADUs unless exempt.
Transit parking exemption
Local ruleYes — no parking required near transit & for conversions
No parking required if within 1/2 mile of public transit or other state exemptions.
Garage-conversion replacement parking
Local ruleNot required
No replacement parking required for garage/carport conversion.
Approval, timeline & cost
Approval path
CA state lawMinisterial (by right)
No public hearing or discretionary design review for a qualifying ADU.
Approval timeline
CA state law60 days
The agency must act within 60 days of a complete application — and the ADU is deemed approved if it does not.
Owner-occupancy
Local ruleOnly for a JADU
No owner-occupancy for ADUs; JADUs require owner-occupancy in either JADU or primary.
Impact-fee waiver
Local ruleWaived under 750 sq ft
ADUs up to 750 sq ft exempt from impact fees.
Permits required
Local ruleBuilding permit
Building permit required; must comply with all applicable building codes.
Los Altos-specific factors that can change the answer
State law sets the floor, but these local conditions often decide whether a specific parcel works.
Historic properties
ADUs on historic properties subject to ministerial review for design compliance with Secretary of Interior’s Standards; no Historic Commission review required.
Fire sprinklers
Sprinklers not required for ADUs unless required for the primary dwelling.
Los Altos allows up to 2 JADUs per single-family lot and limits detached ADUs on multifamily lots to 2 per lot. Historic properties require ministerial design review for ADUs, but no commission hearing.
Frequently asked questions
Can I build an ADU in Los Altos?
Yes. California's statewide ADU law requires Los Altos to approve a qualifying accessory dwelling unit ministerial (by right), plus a junior ADU (JADU) on a single-family lot.
How big can an ADU be in Los Altos?
A detached ADU of at least 1,200 sq ft must be allowed, and an ADU of 800 sq ft can never be zoned out by floor-area or lot-coverage limits. A JADU can be up to 500 sq ft.
What are the setback requirements for an ADU in Los Altos?
Side and rear setbacks are limited to 4 ft. per base zone unless physically precluded; then city must allow ADU elsewhere.
Is parking required for an ADU in Los Altos?
Up to 1 space. No parking can be required within ½ mile of transit, for conversions, or for units inside the primary home. When a garage is converted, replacement parking is not required.
How long does ADU approval take in Los Altos?
A complete application must be acted on within 60 days, with ministerial (by right) — no public hearing or discretionary design review for a qualifying ADU.
Do I have to live on the property to build an ADU in Los Altos?
Owner-occupancy: only for a jadu. ADUs under 750 sq ft are also exempt from impact fees.
Sources
- Los Altos Municipal Code Chapter 14.14 (Ord. No. 2024-512, effective April 30, 2024)
- §14.14.050
- §14.14.070
- §14.64.090
- §14.14.060, Footnote 1
- §14.14.100
- §14.14.090(M)
- §14.14.090(D)
- §14.14.090(J)
- §14.14.090(B)
- Cal. Gov. Code §§ 66310–66342 (ADU Law)
- HCD 2025 Accessory Dwelling Unit Handbook
- Cal. Gov. Code § 66317 (ministerial approval, 60-day deadline)
- Cal. Gov. Code § 66321 (size minimums & height)
- Cal. Gov. Code § 66323 (by-right ADU/JADU, 800 sq ft, 4-ft setbacks)
Last updated April 30, 2024. This is an AI-assisted summary of Los Altos's ADU rules, drawn from its published ordinance and California ADU law — general information, not legal advice, and it may be incomplete or out of date. Verify the controlling rule for your specific parcel with Los Altos Planning before relying on it.
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